1. Field of the Invention
The present invention relates to a vacuum suction apparatus for supplying a negative pressure to an operating device such as a suction pad or the like.
2. Description of the Related Art
Heretofore, for example, a vacuum suction apparatus has been known, which is used in workpiece transport mechanisms, positioning mechanisms, and the like. Such a vacuum suction apparatus, as disclosed in Japanese Laid-Open Patent Publication No. 11-226679, includes an ejector that generates a negative pressure from a supplied pressure fluid, the ejector being connected to a suction mechanism made up of a suction pad or the like, whereby a workpiece is attracted under suction by the suction mechanism by the negative pressure generated by the ejector. In addition, transporting of the workpiece is carried out, such that the workpiece is displaced while the attracted state thereof is maintained, and further, the workpiece is released at a predetermined position by releasing the suction state under which the workpiece is attracted.
Incidentally, in general, with this type of vacuum suction apparatus, even after the workpiece has been attracted by the suction mechanism, the pressure fluid is continuously supplied at a fixed amount to the ejector to generate a negative pressure in the ejector. However, since the workpiece has already been attracted under suction by the suction mechanism, further supply of negative pressure from the ejector is not needed, and the pressure fluid supplied to the ejector is simply consumed needlessly. Stated otherwise, with a conventional vacuum suction apparatus, a fixed amount of pressure fluid normally is required to be supplied continuously, regardless of the negative pressure condition supplied to the suction pad.
Accordingly, in recent years, there has been a demand to decrease the amount of pressure fluid consumed, as well as reduce the energy required, when a workpiece is attracted under suction.